The Effect of HIV-1 and Accessory Proteins on Monocyte Derived Dendritic Cell Maturation and Function

Abstract

Dendritic cells (DCs) are specialized members of the innate immune system that are responsible for the initiation of primary adaptive immune responses whose purpose is to resolve infection and inflammation. During most viral infections, mature dendritic cells present critical viral antigens to naïve T-cells within secondary lymphoid organs, resulting in the generation of an antigen-specific adaptive immune response and clearance of the virus. During infection with HIV-1 however, the virus is not cleared and a chronic systemic infection develops characterized by immune dysfunction, CD4+ T-cell depletion, systemic inflammation, and opportunistic infections. A growing body of evidence indicates that HIV-1 subversion of DCs contributes to both HIV-1 pathologies and viral dissemination. A number of similar effects by accessory HIV-1 peptides on DC physiology have also been reported. In vitro studies demonstrate that HIV-1 inhibits DC maturation and function. Ex vivo studies on the other hand describe partially mature, dysfunctional DCs collecting in secondary lymphoid organs. In vitro studies examining the effects of HIV-1-Tat and HIV-1-Vpr have described opposing effects on DC maturation. Therefore we undertook experiments to comprehensively describe the effects of HIV-1 and the Tat and Vpr accessory peptides on DC maturation and function. To understand the contributions of individual viral proteins to DC dysfunction we infected DCs with a dual tropic HIV-1 and examined phenotypic and functional changes after maturation with inflammatory cytokines. Following this we examined the influence of exogenous and endogenous HIV-1-Tat and HIV-1-Vpr on MDDC maturation and function using recombinant proteins and deletion mutant lab adapted HIV-1 strains. Live dual tropic HIV-1 was found to selectively inhibit aspects of phenotypic maturation as well as antigen capture and presentation functions. MDDC MAPK responsiveness to bacterial LPS remained intact however. Exogenous accessory HIV-1 Tat and Vpr did not affect MDDC phenotype but inhibited dextran endocytosis and viral peptide presentation. HIV-1-gp120 increased iMDDC maturation while blunting cytokine induced decreases in MDDC antigen capture abilities. The deletion of HIV-1-Tat did not affect MDDC phenotype, but was found to affect antigen capture decreases by R5 tropic HIV-1BaL. Deletion of HIV-1-Vpr likewise did not affect MDDC phenotype, however it was found to be influential in HIV-1 induced decreases in MDDC antigen presentation to autologous T-cells. These accumulated results indicate that HIV-1 subverts DC maturation and function through whole virus effects and individual accessory peptide influences. Understanding the mechanisms of DC dysfunction in HIV infection may provide some insight into infection prevention strategies and therapies leading to adaptive immune system activation and viral clearance.